Fix system install (detect mbr)

install/variables/disk.py

@@ -1470,7 +1470,8 @@ class VariableOsInstallMbr(LocationHelper,Variable):
             # search /boot device or / device, by priority /boot,/
             if bootDevice:
                 return bootDevice
-        return self.Select('os_device_dev',where='os_device_type',eq='hdd')
+        return [self.Select('os_device_dev',where='os_device_type',eq='hdd',
+                           limit=1)]
 
     def choice(self):
         deviceParentMap = dict(self.ZipVars('os_device_dev','os_device_name'))